1. Field of the Invention
This invention relates to the field of data processing systems. More particularly, this invention relates to the control of communication between a master device and a slave device using permission tokens.
2. Description of the Prior Art
It is known to connect one or more master devices with one or more slave devices via communication circuitry that can take a variety of different forms. For example, on-chip communication may be provided by bus structures designed to provide efficient and robust communication. A problem in these systems is that it can be difficult to introduce a new slave device, or to change a slave device, without requiring significant engineering effort to reconfigure and revalidate the communication mechanisms. In particular, a slave device will typically be limited in the number of concurrently pending messages which is can accept from the communication circuitry (e.g. the number of messages it can buffer at any given time). In order that the slave device can effectively manage communication with the other devices with which it communicates, the slave device typically needs to be customised or configured to match the characteristics of those other devices, e.g. to track how many other devices have attempted to communicate with the slave device and then issue appropriate retry requests in due course. One approach would be to provide the slave device with an excess of capability for communicating with other devices, but this would be wasteful in terms of circuit area overhead and power consumption. Another approach is to customise the slave device for each situation, but this is wasteful of engineering time.